Process of preparing dicarboxylic acid chlorides



Patented Oct. 27, 1953 UNITED STATES TENT OFFICE PROCESS OF PREPARINGDICARBOXYLIC ACID CHLORIDES No Drawing. Application March 14, 1952,Serial No. 276,691

9 Claims.

This invention relates to a new method of preparing dicarboxylic acidchlorides.

The usual methods of preparing acid chlorides from carboxylic acidsconsist in reacting the acid with thionyl chloride, phosphorustrichloride or phosphorus pentachloride. All of these reagents generateundesirable by-products. It has been proposed in the patent literatureto use in their place, phosgene (carbonyl chloride) with appropriatereaction catalysts. This method is reported to be quite satisfactory inthe preparation of monocarboxylic acid chlorides from monocarboxylicacids provided suitable catalysts are used, particularly with the highermolecular weight acids. However, there is no published report thatdicarboxylic acid chlorides have been obtained from dicarboxylic acidsand phosgene, with or without the use of catalysts. The fact is, as willbe shown later, that the published methods of reacting phosgene withcarboxylic acids, which are successful in the treatment ofmonocarboxylic acids, fail utterly to give dicarboxylic acid chlorideswhen applied to dicarboxylic acids.

It has now been found that dicarboxylic acid chlorides can be preparedin excellent yields by reacting dicarboxylic acids with phosgene underspecific conditions, with the added advantage that no reaction catalystsneed be used.

The principal object of the present invention is an improved process forpreparing dicarboxylic acid chlorides. A further object is thepreparation of dicarboxylic acid chlorides by means of phosgene. Otherobjects will appear from the following detailed description of theinvention.

This invention is a process for preparing dicarboxylic acid chlorideswhich comprises reacting a dicarboxylic acid with phosgene in the ratioof at least two moles of phosgene per mole of dicarboxylic acid, thereaction being carried out under a phosgene pressure of at least 10atmospheres and at a temperature of at least 100 C. but below thedecomposition point of the dicarbcxylic acid chloride.

The reaction is represented by the equation where R is a divalentorganic radical.

The method is illustrated in greater detail in the following examples,in which parts are by weight unless otherwise specified.

EXAMPLE I A corrosion-resistant pressure vessel was charged with 83parts (0.5 mole) of terephthalic acid, sealed, cooled, evacuated andcharged with 147 parts (1.5 moles) of phosgene from a storage cylinder.The reaction vessel was heated and agitated at 200 C. under autogenouspressure for 5 hours. After cooling and venting the gases, the reactionproduct (98 parts of solid material) was removed and distilled. Therewas obtained 93 parts (96% yield) of terephthaloyl chloride distillingat133-136 C. at 11 mm. pressure and melting at 84.5 C.

In comparison, an attempt was made to react terephthalic acid withphosgene by a published procedure for preparing monocarboxylic acidchlorides, as follows. Terephthalic acid (67 parts, 0A mole) in finelydivided crystalline form was arranged in a vertical column whichmeasured 22 cm. deep by 3.5 cm. in diameter and was heated to 203 C.while phosgene (1.2 moles) was passed upward through it at a constantrate of flow (0.3 mole per hour) for 4 hours at atmospheric pressure.The terephthalic acid did not liquefy during this treatment but wasrecovered unchanged in its original powdery condition. Consequently,there was no detectable amount of terephthaloyl chloride produced sincethe latter is a liquid at temperatures above C.

EXALQPLE II Following the procedure of Example I, a mixture of 73 parts(0.5 mole) of adipic acid and 147 parts (1.5 moles) of phosgene washeated with agitation at C. under autogenous pressure for 5 hours. Therewas obtained 84 parts (92% yield) of adipyl chloride distilling at 114C. at 9 mm. pressure.

In comparison, an attempt was made to react adipic acid with phosgeneunder conditions reported to produce acid chlorides from monocarboxylicacids, as follows: Adipic acid (73 parts, 0.5 mole) in finely dividedcrystalline form was arranged in a vertical column that measured 13 cm.deep by 3.5 cm. in diameter and was heated to 122-123 C. while phosgene(1.5 moles) at atmospheric pressure was passed upward through it at aconstant rate of flow (0.3 mole per hour) for a period of 5 hours.During this treatment the crystals gradually became sticky but theamount of adipyl chloride that formed, if any, was negligible since themelting point of the product was -147" C. Pure adipic acid melts at151-153 C. while adipyl chloride is a liquid at room temperature andadipic anhydride melts in the range of 20-85 0., depending upon itsdegree of polymerization.

In a further comparative experiment, one of the catalysts disclosed asfavoring the formation of acid chlorides from monocarboxylic acids wasused as follows: A suspension of 73 parts (0.5 mole) of adipic acid in65 parts of xylene containing 5 parts of pyridine, added as catalyst,was heated to 122-123 C. and phosgene (1.8 moles) at atmosphericpressure was bubbled through it at the rate of 0.5 mole per hour for aperiod of 3.5 hours. The adipic acid gradually dissolved and a clearyellow solution resulted midway through the treatment. On distillationunder reduced pressure, a trace (less than 2%) of liquid was collectedin the approximate boil-a ing range of adipyl chloride, but essentiallyall of the reaction product was a non-distillable black tar.

In the process of this invention there can be used any desireddicarboxylic acid, whether it be aliphatic, alicyclic, aromatic,aliphatic-aromatic .or-heterocyclic. The nature and size of theremainder of the molecule are largely immaterial. It is of coursedesirable to use an acid free from Substituents reactive with phosgene,acid chlorides, or hydrogen chloride under the reaction conditions, inorder to avoid interfering side reactions, Additional examples ifsuitable dicarboxylic acids include oxalic acid, malonic acid, succinicacid, methylsuccinic acid, 2,5-dibromo- .adipic acid, p methyladipicacid, pimelic acid, se-

bacic acid, 1,18-octadecanedioic acid, maleic acid,aoctylenadicarboxylic acid, glutaconic acid, muconic acid, acetonedicarboxylic acid, diglycolic acid, suliodiacetic acid, sulfodibutyricacid, cyclobutane 1,4 dicarboXylic acid, cyclohexanel 1,4 dicarboxylicacid, tetrahydrofurane 2,5- dicarboxylic acid, phthalic acid,B-chlQrophthalic acid, isophthalic acid, naphthaline 1,4 dicarboxylicacid, diphenyl 4., dicarboxylic acid, diphenylrnethane eA-dicarboxylicacid, homoterephthalic acid, fl-(i-carboXtmhenyl)propionic acid,phcnylsuccinic acid, benzylmalonic acid, benzophenone irl'-dicarboxylicacid, diphenylsu1f0ne=lA:dicarboxylic acid, diphenyl ether- QAdicarboxylic acid, isocinchomeronic acid, quinolinic acid, ethylenedioxyacetic acid. The preferred starting materials are thosedicarboxylic acids in which the carboxyl groups are separated by ahydrocarbon chain or by a hydrocarbon chain interrupted by ether oxygen,car- .bonyl or sulfonyl groups, or in which the carboxyl groups areattached to an aromatic or cyclic group. Another preferred embodiment isthe use of mixtures of more than one of such kinds, for instance,mixtures of isophthalic and torephthalic acids, or mixtures ofterephthalic with isocinchomeronic acid. The most ready availablestarting materials are those dicarboxylic acids which, apart from thecarboxyl groups, contain only carbon and hydrogen. In this class, thepreferred materials are the dicarboxylic acids having a total of 2 tocarbon atoms.

For good results, it is desirable to use at least 2 moles of phosgeneper mole of dicarboxylic acid. Preferably, a moderate excess over thestoichiometrical amount is used, for example, between 2,2 and a moles ofphosgene per mole of dicarhoxylic acid. Larger excesses of phosgene canbe used if desired but there is no advantage in doing so.

The use of a superatmospheric phosgene pressure is critical, as has beenshown. For good results, the phosgene pressure in the system sh uld beat least about 10 atmospheres. Preferably, it is between about 12 and100 atmospheres. However, the pressure can be as high as the equipmentwill withstand. The desired pressures are conveniently achieved simplyby operating in closed vessels under the autogenous pressure of phosgeneat the operating temperature. The vapor pressure of phosgene is 13.8atmospheres at 0., 34.4 atmospheres at C. and 56 atmospheres at 182 0.,its critical temperature. It should be noted that the total pressure inthe system will be higher than the vapor pressure of phosgene as thereaction progresses since two molecules of gas are formed for eachmolecule of phosgene which reacts. If desired, extraneous pressure ofeither phosgene or another gas, such as carbon dioxide or nitrogen, canbe imposed on the system, but this is in general unnecessary.

The reaction proceeds only slowly at temperatures below about 100 C. andit is therefore desirable to operate above that temperature. The limi infactor with respec o the temperat r is the decomposition point of thedicarboxylic acid chloride. In some cases, this is rather low. Forexample, adipyl chloride has a tendency to decompose above about 150 C.and it is advisable to operate bel w that temperature n h s case- On theother hand, many dicarboxylic acid chlorides such as terephthaloylchloride are quite stable at high temperatures. The decomposition pointor most dicarb xylio c d chlorides c n be found in the literature; if ni is a matter o a very simple test to ascertain a safe temperaturelimit. Provided the decomposition point is not reached, a usefultemperature range for the reacon is b ween .100 and. 2 0 The r c iontime will, of course, depend at least partly on the starting materialbut, in general, a reaction time of one to six hours will be sufiicientto obtain good yields.

A ha been sh wn, thi m thod ha he reat advantage that no reactioncatalysts need be used, thus simplifying the operations and dercreasinthe costs. If desired, however, the cata lysts proposed by priorinvestigators in connection with the preparation of monocarboxylic acidchlorides can b u d- It is in g ne al unnecessary to u reaction solventsor diluents. If desired, however, suitable inert me ia. liqu d a threaction temp ra ure, can be used. such as aliph ti r romatic hydocarbon or halo en ydr bons, e. a. n-hcxane. ker sen nz n t lu ne. cabon t rachlori e, te rachloroethane nd the like- Isolation of he d arbxylic acid c oride c n be carried out by any suitable means, such asdistillation under reduced pressure or crystallization from anappropriate lv nt- S n he y ld are in eneral n a ly q ant ve. h crreaction product, can often be used directly without furthe tr atment.

While the process of this invention is normally carried out batch-wisein corrosion-resisting autoclaves, it can also be carried out in acontinuous manner using a flow system where the a ion mix ur i in he hozon for only a short period of time before being discharged. This isparticularlyadvantageous when the dicarboxylic acid or chloride issensitive to hydrogen chloride.

This invention provides a simple and economical method of preparingdicarboxylic acid chloride from the corresponding acids. As is known,these materials are of considerable use as intermediates in thepreparation of many valuable monomeric or polyme c chemicals- It will beappreciated that many modifications may be made in the processesdescribed in the foregoing without departing from the scope or spirit ofthe invention. I intend to be limited only by the following patentclaims:

I claim:

1. The process of preparing dicarboxylic acid chlorides which comprisesreacting a dicarboxylic acid with phosgene in the ratio of at least 2moles of phosgene per mole of dicarboxylic acid, the reaction beingcarried out under a phosgene pressure of at least 10 atmospheres and ata temperature of at least 100 C. but below the decomposition point ofthe dicarboxylic acid chloride.

2. The process of claim 1, wherein the phosgene pressure is between 12and 100 atmospheres.

3. The process of claim 1, wherein the temperature is between 100 and250 C.

4. The process of claim 1, wherein the reaction time is from 1 to 6hours.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,013,988 Meder et a1. Sept. 10, 1935 2,013,989 Meder et a1Sept. 10, 1935 2,567,132 Stilmar Sept. 4, 1951

1. THE PROCESS OF PREPARING DICARBOXYLIC ACID CHLORIDES WHICH COMPRISESREACTING A DICARBOXYLIC ACID WITH PHOSGENE IN THE RATIO OF AT LEAST 2MOLES OF PHOSGENE PER MOLE OF DICARBOXYLIC ACID, THE REACTION BEINGCARRIED OUT UNDER A PHOSGENE PRESSURE OF AT LEAST 10 ATMOSPHERES AND ATA TEMPERATURE OF AT LEAST 100* C. BUT BELOW THE DECOMPOSITION POINT OFTHE DICARBOXYLIC ACID CHLORIDE.